Absorptive structure having tapered capillaries

ABSTRACT

Absorptive devices, such as disposable diapers, presenting a dry surface feel to the user. The surface feel is obtained when the topsheet is a liquid impervious material provided with tapered capillaries of critical diameters and tapers, each capillary having a base in the plane of the topsheet and an apex remote from the plane of the topsheet, and when each apex is in intimate contact with an absorbent pad.

United States Patent 1191 Thompson 1 51 Dec. 30, 1975 1 1 ABSORPTIVESTRUCTURE HAVING TAPERED CAPILLARIES [52] US. Cl. 128/287; 128/156;128/296 [51] Int. C1. A4113 13/02 [58] Field of Search 128/287, 286,156, 296,

3,399,672 9/1968 Crowe, Jr. et a1. 128/156 3,814,101 6/1974 Kozak128/287 FOREIGN PATENTS OR APPLICATIONS 2/1973 Germany 128/287 PrimaryExaminerRichard A. Gaudet Assistant ExaminerJ. Yasko Attorney, Agent, orFirm-Monte D. Witte; Fredrick H. Braun; John V. German [57] ABSTRACTAbsorptive devices, such as disposable diapers, presenting a dry surfacefeel to the user. The surface feel is obtained when the topsheet is aliquid impervious material provided with tapered capillaries of criticaldiameters and tapers, each capillary having a base in [56] ReferencesCited th 1 fm t h t d mote f m th e p 3116 0 e OPS ee an an apex 1'6 1'0e UNITED STATES PATENTS plane of the topsheet, and when each apex is ininti- 2,923,298 2/1960 Dockstader 61 a1 128/296 mate Contact with anabsorbent pad, 3,221,738 12 1965 Ekberg et a1. 3,292,619 12 1966 Egler128/156 8 Claims, 4 Drawing g \l I A 3 US. Patent Dec. 30, 19753,929,135

Fig. 4 26 ABSORPTIVE STRUCTURE HAVING TAPERED CAPILLARIES BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates totopsheets for absorptive devices such as diapers, sanitary napkins, bedpads, incontinent pads, towels, bandages and the like, and,

more particularly, to absorptive structures which freely allow fluid topass into the interior of an absorptive device but which inhibit thereverse flow of fluid. A topsheet is the portion of an absorptive devicewhich covers one face of the absorbent element of an absorptive deviceand which in some applications contacts the skin of the person using theabsorptive device.

2. Description Of The Prior Art Absorptive devices are articles ofmanufacture designed to receive and retain fluid discharges from thebody within an absorbent element of the absorptive device. Absorptivedevices such as diapers, sanitary napkins, catamenial tampons, bed pads,incontinent pads, towels, bandages and the like are well known articlesof commerce. In recent times, single use disposable absorptive deviceshave significantly replaced permanent absorptive devices which aredesigned to be laundered and reused. While the improved absorptivestructure of this invention can be used with reusable absorptivedevices, it finds great utility when used with disposable absorptivedevices and will be discussed in that context.

Disposable absorptive devices comprising an absorbent pad covered with atopsheet which contacts the body are well known. Covering the outerportion of the absorptive device with a fluid-impermeable backsheet toprevent absorbed fluids from leaking out of the absorptive device andsoiling clothing, bed clothes, etc. is equally well known. The absorbentpad component of disposable absorptive devices can comprise well knownmaterials such as creped cellulose wadding, airlaid felt or the like.The liquid impermeable backsheet can comprise any of various materialswell known in the art such as polyethylene film.

One of the principle disadvantages of conventional absorptive devices isthe maceration of the skin caused by prolonged contact with absorbedfluids. One especially common manifestation of this maceration is diaperrash generally occurring about the base of the trunk of infants. Inorder to minimize the effect of prolonged liquid contact with the skin,absorptive devices such as diapers have been produced with the bodycontacting topsheet thereof designed to exhibit a greater or lesserdegree of surface dryness. For example, U.S. Pat. No. 3,327,625 issuedto Johnson on Mar. 1, 1966, teaches that any hydrophobic material in thecrotch area of the diaper will cause moisture to wick away from the skinof an infant wearer and thereby provide a substantially dry surface incontact with the infants skin. U.S. Pat. No. Re. 26,151 issued to Duncanet al. on Jan. 31, 1967, teaches the use of porous, hydrophobic,nonwoven fabrics as topsheets. U.S. Pat. No. 2,916,037 issued to Hansenon Dec. 8, 1959, is a further example of the use of a non-woventopsheet.

U.S. Pat. No. 3,814,101 issued to Kozak on June 4, 1974, attacks theproblem of a wet topsheet in a manner slightly different from the use ofhydrophobic nonwoven materials. Kozak suggests a topsheet of anonfibrous hydrophobic film which is provided with a plurality ofvalvular slits which restrict the reverse flow of liquid from theabsorbent element of the device.

Sisson, in Belgian Patent 811,067, Aug. 16, 1974, which claims priorityfrom U.S. patent application Ser. No. 333,1l0, Feb. 16, 1973, describesa breathable, liquid impervious backsheet containing apertured bosses.The apertures therein, so as to maintain the liquid impervious characterof the backsheet, are smaller in diameter than the capillarieshereinafter described.

SUMMARY OF THE INVENTION This invention concerns an absorptive structurefor absorptive devices such as diapers, sanitary napkins, catamenialtampons, bed pads, incontinent pads, bandages and the like. Theabsorptive structure of this invention comprises a fluid-impervioustopsheet material provided with tapered capillaries or orifices ofcritical opening dimensions and of critical angles of taper, each ofwhich has a base in the plane of the topsheet and an apex remote fromthe plane of the topsheet, and the apex of which is in intimate contactwith an absorbent element. The critical angle of taper is from about 10to about 60; base opening dimension is from about 0.006 to about 0.250inch; apex opening dimension is from about 0.004 to about 0.100 inch.

The topsheet of this invention is an improvement over prior arttopsheets in that it allows the free transfer of fluids from the bodyinto the absorbent element of the device while inhibiting the reverseflow of these fluids thereby providing a relatively much dryer surfacein contact with the user than has been previously obtainable. Whiledirected primarily to single use, disposable absorptive devices such asdisposable diapers, the

absorptive structure of this invention can be used with reusableabsorptive devices such as cloth diapers.

Accordingly, it is an object of this invention to provide an absorptivestructure for absorptive devices which permits the free transfer offluids from the body into the absorbent element of the absorptive devicewhile effectively inhibiting the reverse flow of fluids from theabsorbent element.

It is a further object of this invention to provide a topsheet forabsorptive devices which presents to the user thereof a dryer surfacethan has been previously obtainable.

It is a further object of this invention to provide a topsheet forabsorptive devices which is comfortable when in contact with the skin ofthe user.

It is a still further object of this invention to provide a disposablediaper which presents a surface to the wearer thereof which is dryerthan has been previously obtainable.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes withclaims particularly pointing out and distinctly claiming the subjectmatter of the present invention, it is believed that the invention canbe more readily understood from the following description taken inconnection with the accompanying drawings, in which:

FIG. 1 is a perspective representation of an unfolded disposable diaperwith portions of its components cut away.

FIG. 2 is an enlarged fragmentary perspective view of a taperedcapillary as used in this invention.

FIG. 3 is a cross-section in elevation of a tapered capillary takenalong the line 33 in FIG. 2.

3 FIG. 4 is the cross-section of a tapered capillary as shown in FIG. 3,but here shown in initmate contact with an absorbent element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The discussion thatfollows is primarily directed to the use of the invention as a uniqueabsorptive structure embodied in a disposable diaper. While this iscontemplated as being a preferred use of the absorptive structure, itshould be understood that it also has substantial utility in a widevariety of absorptive devices, both disposable and reusable, such assanitary napkins, catamenial tampons, bed pads, incontinent pads,towels, bandages and the like. The detailed description of theabsorptive structure and its use in a disposable diaper will allow oneskilled in the art to readily adapt this invention to other devices.

FIG. 1 is a perspective view of a disposable diaper in an unfoldedcondition. Various layers have been cut away to more clearly show thestructural details of this embodiment. The disposable diaper is referredto generally by the reference numeral 21. The novel topsheet of thisinvention is shown at-22. The other two major components of thedisposable diaper 21 are the absorbent element or pad 23 and thebacksheet 24. In general, the side flaps 25 of the backsheet 24 arefolded so as to cover the edges of the absorbent pad 23 and topsheet 22.Topsheet 22 is generally folded to completely enclose the ends ofabsorbent pad 23. The drawing of diaper 21 in FIG. 1 is a simplifiedrepresentation of a disposable diaper. A more detailed description of apreferred embodiment of a disposable diaper is contained in theaforementioned US. Pat. No. Re. 26,151 which is herein incorporated byreference.

The topsheet 22 of this invention is constructed from a liquidimpervious material. An example of a suitable liquid impervious materialis low density polyethylene of from 0.001 to 0.002 inch (0.0025 to0.0051 centimeter) thickness. The topsheet 22 is provided with taperedcapillaries as hereinafter described.

Tapered capillaries 26 are shown in perspective in FIG. 2 and incross-section in FIG. 3. While tapered capillary 26 is shown in FIGS. 2and 3 as generally in the form of a frustrum of a conical surface, it isto be understood that any generally tapered structure, such as afrustrum of a pyramid or the like with a triangular, square, orpolygonal base, is within the contemplation of the invention; circulartapered capillaries, however, are used in this description forconvenience in explaining the manifold advantages of the invention. Itis also to be understood that the tapered capillaries can be asymmetric(i.e., the angle of taper on one side can be different from that onanother side) and that the angle of taper can change continuously (i.e.be curved) over the distance from base 30 to apex 29. In the lattercase, the angle of taper is defined as the angle of the tangent to theside of the capillary at its point of minimum apex opening dimension.Also included in the term tapered capillary is a slot formed intotopsheet 22, said lot having finite length less than the width oftopsheet 221 and having its sides and ends tapered at angles analogousto those hereinafter described in relation to a circular taperedcapillary.

The angle of taper is represented by a in FIG. 3. The angle of tapersuitable for use in the topsheet of this invention is from about 10 toabout 60.

Base opening dimension, except for the hereinbefore mentioned slot, isdefined as the maximum open measurement in the plane of topsheet 22 attapered capillary 26. Apex opening dimension, except for the hereinbefore mentioned slot, is defined as the maximum open measurement inthe apex of tapered capillary 26 which apex is remote from the plane ofthe topsheet 22. When the tapered capillary is in the form of a frustrumof a conical surface, the base and apex opening dimensions are,respectively, base diameter 28 and apex diameter 27. Base diameter andapex diameter are hereinafter used interchangeably with, respectively,base opening dimension and apex opening dimension.

When the tapered capillary of this invention is in the form of a slothaving a finite length less than the width of the topsheet, base openingdimension and apex opening dimension refer to the minimum openmeasurements in the base of the slot in the plane of topsheet 22 and theapex of the slot remote from the plane of topsheet 22. That is, base andapex opening dimensions refer to the widths rather than to the length ofthe slot.

Tapered capillary apex diameter 27 is a diameter which will allow liquidto readily pass from the surface of topsheet 22 to absorbent pad 23.Apex diameter 27 is from about 0.004 to about 0.100 inch (0.010 to 0.254centimeter), preferably from about 0.005 to about 0.020 inch (0.013 to0.051 centimeter).

Tapered capillary base diameter 28 is selected to satisfy two criteria.The first of these is the subjective feel of the surface of the topsheetwhich contacts the skin of the user. It has been discovered that theaforementioned polyethylene can be made to exhibit pleasing, clothlike,non-waxy attributes when base diameter 28 is within the range from about0.006 to about 0.250 inch (0.015 to 0.635 cemtimeter). Preferably basediameter 28 should be within the range of from about 0.030 to about0.060 inch (0.076 to 0.152 centimeter). The second criterion is that thecapillary base diameter be small enough to allow an expected liquiddroplet to bridge across at least one capillary. This criterion issatisfied by the above dimensions for disposable diapers.

The height of the tapered capillary is defined as the distance betweenthe outermost surface of topsheet 22 (i.e., that surface which normallycontacts the skin of the user) and the apex 29 of tapered capillary 26.This height, of course, depends upon apex diameter 27, base diameter 28,and angle of taper a which have been selected as hereinbefore described.The height of the tapered capillary should provide a structure with aminimum tendency to collapse in use. The characteristics of the materialof construction of topsheet 22 in large measure determine suitableranges for the height. When topsheet 22 is low density polyethylene offrom 0.001 to 0.002 inch thickness and apex diameter 27 and basediameter 28 are in the preferred range, and angle of taper a is in itscritical range, the height of the tapered capillary can be from about0.003 to about 0.159 inch (0.008 to 0.404 centimeter).

It is necessary that the apex 29 of the tapered capillary 26 be inintimate contact with absorbent pad 23.

Practical absorptive devices such as disposable diapers must beconstructed so there is no reverse flow of fluid when the absorbentelement is placed under pres sure as by an infant sitting on or movingabout in a wet disposable diaper. Protection from this pressure inducedreverse flow is obtained if the absorbent element is constructed so asto be less than totally saturated at its expected maximum fluid content.That is tosay, the absorbent elementshould be designed and constructedto contain a significantly larger quantity of fluid than it isanticipated that the absorptive device will be required to contain in apractical use situationfFor the preferred absorptive pad describedhereinafter, a practical anticipated liquid loading of from 3 times to 6times the dry weight of the pad is satisfactory. It should be noted thatthis permissible loading is somewhat higher than that which isacceptable because of surface wetness characteristics when the usualnon-woven topsheet is used with a disposable diaper. One benefit fromthis increased loading is a possible net reduction in the amount ofmaterial used in the absorbent pad of this invention as compared to thatused in ordinary disposable diapers. j I

Another necessary criterion is "apparent to those skilled in the art:the topsheet must allow rapid transfer of liquids through it. This rateof transfer depends on several variables such as rate of fluid dischargefrom the body, viscosity of the fluid, fraction of open area of thetopsheet, minimum diameter of tapered capillaries, etc. The propercombination of parameters for any given application can readily bedetermined by simple experimentation. The preferred dimensions recitedherein for disposable diaper topsheets insure rapid transfer of urineinto the absorbent element.

A state of relative dryness on the surface of the topsheet implies thatmost of the liquid which contacts the topsheet is transferred through itto the absorbent element. This in turn implies that eachisolated-droplet of fluid in contact with the topsheet must be incontact with the base diameter of a tapered capillary. This state ofaffairs can best be achieved if the land area (the area of the topsheetthat exists between the bases of the tapered capillaries) is maintainedat a minimum. The minimum limiting value is the case where conicaltapered capillaries or pyramidal tapered capillaries are provided inclose packed array (where the periphery of the base 30 of each capillaryis in contact on all-sides with the periphery of the base 30 of adjacentcapillaries). The preferred arrangement of minimum land area tends toinsure that an individual droplet will contact at least one taperedcapillary. A preferred arrangement in disposable diapers is where thetapered capillaries as hereinbefore described are in ordered arrangementwith from about 30 to about 1500 tapered capillaries per square inch oftopsheet (5 to 231 per square centimeter).

Topsheet 22 provided with tapered capillaries 26 can be manufactured inany of several ways well known in the art. One particularly suitablemethod is to provide a heated mold with male elements of the shape andarrangement of the desired tapered capillaries (hereinafter a pin mold).Each male element is secured in such a fashion that its apex extendsaway from the base of the mold. A portion of liquid-impervious materialis brought into contact with the heated mold between the mold and aresilient backing plate. Pressure is applied to the combination of mold,liquid impervious material and resilient back plate and taperedcapillaries are formed in the liquid impervious material to make thetopsheet of this invention. An alternate way of constructing thetopsheet of this invention is to subject a portion of liquid-imperviousmaterial to vacuum forming over an appropriate mold by means well knownin the art. A third way of making topsheet 22 for use in this inventionis to cast the topsheet on a mold designed for the purpose and similarto that previously described. After forming tapered capillary structuresin one of the three aforementioned ways, it may be necessary tophysically remove material from the apex of the tapered capillarystructure so as to insure that the apex diameter is the desired value.Such removal of material can be accomplished by, for example, subjectingthe apex to controlled abrasion or by heating the formed topsheet so asto melt open the apex.

Absorbent pad 23 of the diaposable diaper exemplified in FIG. 1 cancomprise materials commonly used in absorptive devices and well known tothe art. A preferred form of suitable absorbent material for the pad 23is the use of comminuted wood pulp generally referred to as 'airfelt.When airfelt is used, the tissue paper envelope commonly present indisposable diaper applications can be omitted. Other materials can alsobe used for the absorbent pad 23 such as a multiplicity of plies ofcreped cellulose wadding and any equivalents thereof.

As described hereinbefore, absorbent pad 23must be in contact with theapex 29 of the tapered capillary 26 of the topsheet of this invention.Further, the absorbent pad 23 must preferentially absorb the liquid fromapex 29 of the tapered capillary 26.

Liquid impervious backsheet 24 can be any material well known in theart. A preferred material is low density polyethylene 0.001 to 0.002inch (0.0025 to 0.0051 centimeter) thick.

The elements of the finished disposable diaper tapered capillarytopsheet 22, absorbent pad 23 and optional elements such as fluidimpervious backsheet 24 can be assembled into a practical, economicaldisposable diaper by means well known in the'art. An example of suchunion into disposable diapers is admirably described in the hereinbeforeincorporated US. Pat. No. Re. 26,151.

As noted, the tapered capillary topsheet of this invention has beendescribed interms of a disposable diaper. Other absorptive devices wellknown in the art such as sanitary napkins, catamenial tampons, bed pads,incontinent pads, towels, bandages and the like can be advantageouslyconstructed using the tapered capillary topsheet of this invention.Specific examples of sanitary napkins and catamenial tampons wherein thetopsheet of this invention can be used can be found in US. Pat. No.3,800,797 issued to Tunc on Apr. 2, 1974, and US. Pat. No. 3,815,601issued to Schaefer on June I l, 1974, both of which are hereinincorporated by reference.

In order to contribute to a better understanding of this invention andnot by way of limitation, the following examples are provided.

EXAMPLE I Conical tapered capillaries having a base diameter of 0.040inch and an apex diameter of 0.012 inch and an angle of taper of 45 wereformed with a pin mold into a sheet of 0.0015 inch thick Surlyn, aliquid impervious ionomer film made by the E. I. du Pont de Nemours andCompany. A total of 722 capillaries per square inch in regular arraywere impressed into the film. The topsheet was placed so that the apicesof the tapered capillaries were in contact with an absorbent pad madefrom airlaid softwood fibers. The resulting absorbent structure alloweddroplets of saline solution to pass through the topsheet into theabsorbent pad. The free surface of the topsheet exhibited a dry feel andwas pleasing to the touch.

EXAMPLE [1 Example 1 is repeated, except that 320 conical taperedcapillaries having a base diameter of 0.060 inch and an apex diameter of0.012 inch and an angle of taper of 45 are formed in a regular arrayinto each square inch of respectively, Surlyn, and low densitypolyethylene 0.0015 inch thick. Essentially the same results areobserved.

EXAMPLE Ill Pyramidal tapered capillaries having a square base 0.050inch on each side and a square apex 0.012 inch on each side and an angleof taper of 45 were embossed into 0.0015 inch thick low densitypolyethylene film. A total of 400 tapered capillaries per each squareinch of film were used. Essentially the same results as in Example 1were observed when the topsheet was placed in proper contact with theairfelt of Example 1. Further, this absorbent structure was used in theconstruction of a disposable diaper according to the teaching of Duncanet al. in the aforementioned Re. 26,121. When used in a practical way oninfants, the disposable diaper exhibited a drier, more comfortablesurface in contact with the infant than can be obtained with aconventional hydrophobic nonwoven topsheet.

EXAMPLE 1V Example 11, including the bringing of the apices of theformed cones into contact with an absorbent airfelt, is repeated usingformed cones having base diameter, apex diameter, angle of taper, andnumber of capillaries per square inch, respectively, as follows: 0.030inch, 0.010 inch, 45, 1280; 0.060 inch, 0.012 inch, 60, 320; and 0.100inch, 0.015 inch, 30, 74. Satisfactory results in terms of transfer offluid and dry surface feel are obtained.

What is claimed is:

l. A disposable diaper comprising a topsheet and an absorbent elementwherein said topsheet is a liquidimpermeable material provided withtapered capillaries each'having a base in the plane of said topsheet andan apex remote from said plane of said topsheet, having an angle oftaper of from about 10 to about 60, base opening dimension of from about0.006 to about 0.250 inch, and apex opening dimension of from about0.004 to about 0.100 inch; and wherein said absorbent ele ment is inintimate contact with said apex of said tapered capillaries.

2. The disposable diaper of claim 1 wherein said base opening dimensionis from about 0.030 to about 0.060 inch and said apex opening dimensionis from about 0.005 to about 0.020 inch.

3. The disposable diaper of claim 2 wherein said tapered capillaries arein the form of frustrums of conical surfaces.

4. The disposable diaper of claim 2 which includes as an additionalelement a fluid-impervious backsheet.

5. The disposable diaper of claim 1 which includes as an additionalelement a fluid-impervious backsheet.

6. An absorptive structure for absorbing and containing fluid bodilydischarges comprising a topsheet and an absorbent element wherein saidtopsheet is a liquidimpervious material provided with taperedcapillaries having a base in the plane of said topsheet and an apexremote from said plane of said topsheet, having an angle of taper offrom about 10 to about 60", base opening dimension of from about 0.006to about 0.250 inch, and apex opening dimension of from about 0.004 toabout 0.100 inch; and wherein said absorbent element is in intimatecontact with said apex of said tapered capillaries.

7. The absorptive structure of claim 6 wherein said base openingdimension is from about 0.030 to about 0.060 inch and said apex openingdimension is from about 0.005 to about 0.020 inch.

8. The absorptive structure of claim 7 wherein said tapered capillariesare in the form of frustrums of conical surfaces.

UNI' IED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3 929 135 DATED December 30, 1975 |N\/'ENTOR(S) Hugh A.Thompson It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 54, "3,327,625" should read 3,237,625

Signed and Scaled this Thirty-first Day of May 1977 [SEAL] Arrest:

RUTH C. MASON Atlesting Officer C. MARSHALL DANN Commissioner of Parentsand Trademarks

1. A disposable diaper comprising a topsheet and an absorbent elementwherein said topsheet is a liquid-impermeable material provided withtapered capillaries each having a base in the plane of said topsheet andan apex remote from said plane of said topsheet, having an angle oftaper of from about 10* to about 60*, base opening dimension of fromabout 0.006 to about 0.250 inch, and apex opening dimension of fromabout 0.004 to about 0.100 inch; and wherein said absorbent element isin intimate contact with said apex of said tapered capillaries.
 2. Thedisposable diaper of claim 1 wherein said base opening dimension is fromabout 0.030 to about 0.060 inch and said apex opening dimension is fromabout 0.005 to about 0.020 inch.
 3. The disposable diaper of claim 2wherein said tapered capillaries are in the form of frustrums of conicalsurfaces.
 4. The disposable diaper of claim 2 which includes as anadditional element a fluid-impervious backsheet.
 5. The disposablediaper of claim 1 which includes as an additional element afluid-impervious backsheet.
 6. An absorptive structure for absorbing andcontaining fluid bodily discharges comprising a topsheet and anabsorbent element wherein said topsheet is a liquid-impervious materialprovided with tapered capillaries having a base in the plane of saidtopsheet and an apex remote from said plane of said topsheet, having anangle of taper of from about 10* to about 60*, base opening dimension offrom about 0.006 to about 0.250 inch, and apex opening dimension of fromabout 0.004 to about 0.100 inch; and wherein said absorbent element isin intimate contact with said apex of said tapered capillaries.
 7. Theabsorptive structure of claim 6 wherein said base opening dimension isfrom about 0.030 to about 0.060 inch and said apex opening dimension isfrom about 0.005 to about 0.020 inch.
 8. The absorptive structure ofclaim 7 wherein said tapered capillaries are in the form of frustrums ofconical surfaces.